4,5-Dichloro-2,2,4,5,-tetrafluoro-1,3-dioxolane

ABSTRACT

Perfluoro-1,3-dioxole, prepared by dechlorinating 4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane with magnesium, is a useful monomer, which polymerizes to either amorphous or liquid homopolymers and copolymerizes with tetrafluoroethylene as well as with other monomers to both crystalline and amorphous copolymers having one or more such comonomers incorporated therein. Amorphous homopolymers and copolymers of perfluoro-1,3-dioxole are useful in such applications as glazing for reactors for hydrogen fluoride reactions. Amorphous homopolymers and amorphous or crystalline copolymers form self-supporting films and can be used for coatings and linings which are inert to most chemicals and are stain and weather resistant and as dielectrics for electrical and electronic equipment. Liquid homopolymers can be used as hydraulic fluids and heat exchange media.

CROSS-REFERENCE TO RELATED APPLICATION

This a divisional of my copending application Ser. No. 421,824, filedSept. 23, 1982, now U.S. Pat. No. 4,485,250.

BACKGROUND OF THE INVENTION

This invention is directed to perfluoro-1,3-dioxole (sometimes referredto hereafter as perfluorodioxole or PD), its preparation, and itspolymerization products.

While perfluoro(2,2-dimethyl-1,3-1,3-dioxole) and its polymers are knownfrom U.S. Pat. Nos. 3,865,845 and 3,978,030 to Resnick, the simplestmember of the family, PD, shown in Formula (1) below, has never beenreported: ##STR1##

SUMMARY OF THE INVENTION

According to this invention, there are now provided:perfluoro-1,3-dioxole, homopolymers and copolymers ofperfluoro-1,3-dioxole, and processes for making perfluoro-1,3-dioxole.

DETAILED DESCRIPTION OF THE INVENTION

PD can be conveniently made in four steps from ethylene carbonate, asshown in the following reaction sequence: ##STR2##

Thus, ethylene carbonate (2) is chlorinated in the presence of light totetrachloroethylene carbonate (3), which is fluorinated with sulfurtetrafluoride in the presence of hydrogen fluoride to4,4,5,5-tetrachloro-2,2-difluoro-1,3-dioxolane (4). This compound reactswith either antimony trifluoride or hydrogen fluoride in the presence ofantimony pentachloride to yield4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (5), which isdechlorinated with magnesium to PD (1). This last step is preferablycarried out in the presence of mercuric chloride and iodine.

Another synthetic route starts with 1,3-dioxolane (6), which isperchlorinated to hexachloro-1,3-dioxolane (7), then fluorinated eitherwith antimony trifluoride or with hydrogen fluoride in the presence ofSbCl₅ to (5), which then is dechlorinated as before. This reactionsequence is shown below: ##STR3##

Perfluorodioxole is a gas which boils at about 0° C. Since its toxicityis unknown, it should be treated as a potential health hazard. Inaddition, it is flammable at volume concentrations of about 5-40% inair.

PD forms with tetrafluoroethylene (TFE) tough, crystalline copolymers,suitable as dielectrics in electrical and electronic equipment. The PDcontent in these copolymers ranges from less than 1 to about 12 molepercent, as determined by nuclear magnetic resonance (NMR) spectroscopy.As the PD content increases beyond approximately 12 mole percent, itscopolymers with TFE become amorphous. They can be used in coatings andfinishes resistant to chemicals, stains, and weather.

It sometimes is advantageous to copolymerize PD with TFE and a thirdethylenically unsaturated monomer. Such third monomer may be amongothers an olefin, such as ethylene, propylene, isobutylene, or butene-1;a fluoroolefin, such as vinylidene fluoride, hexafluoropropylene, orchlorotrifluoroethylene; or a monomer carrying a functional group, suchas a perfluoro(alkyl vinyl ether), methyl3-[1-[difluoro[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-2,2,3,3-tetrafluoro-propanoate,and2-[1-[difluoro[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2-tetrafluoroethanesulfonylfluoride.

The presence of a third monomer in the copolymer may lower the copolymercost, for example when either PD of TFE is replaced in part by anolefin. It may change the copolymer's properties, for example, fromcrystalline to amorphous or from non-elastomeric to elastomeric.Finally, the third monomer permits the introduction of functionalgroups, for example fluorosulfonyl or methoxycarbonyl.

Depending on the specific third monomer as well as on the relativeproportions of all comonomers, the terpolymer may or may not becrystalline. There is no absolute numerical line of demarcation whichwould permit to predict the crystalline character of a terpolymer fromthe relative proportions of monomers. As a general guideline, thecrystalline character of a terpolymer increases as the proportion of TFEincreases. Moreover, it is possible to have amorphous terpolymers inwhich the proportion of PD is considerably less than 12 mole % as wellas crystalline terpolymers in which it is well above 12 mole %.

Terpolymers of PD with TFE and another monomer will thus have a broadrange of applications in coatings, in high performance elastomers andplastics and as intermediates to polymers having other functionalgroups.

Dipolymers of PD with monomers other than TFE also are possible,although not all ethylenically unsaturated monomers will copolymerizewith PD in the absence of a third monomer. For example, α-olefins willnot form dipolymers with PD, but fluoroolefins and monomers carrying afunctional group, such as those recited above in connection withterpolymers of PD will copolymerize with PD to form dipolymers. Thepreferred such comonomer, both in PD dipolymers and in terpolymers withPD and TFE is vinylidene fluoride.

While copolymers of PD with TFE and another ethylenically unsaturatedmonomer are the most likely of all terpolymers to find industrialapplications, terpolymers of PD with other ethylenically unsaturatedmonomers also can be made, and this invention is not limited to the useof any specific type or number of monomers that can be copolymerizedwith PD. Obviously, for practical reasons one would not wish to run thepolymerization with an excessive number of monomers, but that is only apractical limitation, rather than a limitation of the invention.

The last step in the preparation of PD, dechlorination of4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (5), is preferablycarried out in a tetrahydrofuran solution. In spite of the largedifference between the boiling points of PD and tetrahydrofuran, whichboils at 65°-66° C., a small amount of tetrahydrofuran (about 1% orless) is usually present in distilled PD. When PD is further purified,for example, by aqueous extraction followed by distillation on aspinning band column, it has a tendency to polymerize spontaneously attemperatures of about room temperature to about -5° C. Highly purifiedPD polymerizes spontaneously even in a dry ice chest. PD homopolymersare amorphous solids. When made in the presence of small amounts oftetrahydrofuran, for example, 2% of the weight of PD or less, they havea glass transition temperature, Tg, within the range of about 84°-92°C., while the homopolymers made in the absence of tetrahydrofuran havetwo Tg's, at about 172°-179° C. and 212° C.

Amorphous homopolymers and copolymers of PD are useful in glazingreactors for hydrogen fluoride reactions. Amorphous homopolymers andamorphous or crystalline copolymers of PD form self-supporting films andcan be used for coatings and linings which are inert to most chemicalsand are stain and weather resistant and as dielectrics for electricaland electronic equipment.

When allowed to stand at room temperature with modest amounts oftetrahydrofuran, for example, 10-100% of the weight of PD, PD forms lowmolecular weight polymers, which are greases or liquids. They aresuitable in such applications as hydraulic fluids, lubricants, and heatexchange media.

This invention is now illustrated by the following examples of certainrepresentative embodiments thereof, where all parts, proportions, andpercentages are by weight unless otherwise indicated.

Synthesis of PD (a) Tetrachloroethylene Carbonate (3)

A 1000 mL creased flask equipped with a stirrer, a thermometer, a gasinlet tube, and a water condenser topped by a dry ice condenser, wascharged with 352.4 g (4 moles) of melted ethylene carbonate. Theapparatus was purged with nitrogen while stirring and heating to 50° C.After turning off the nitrogen, chlorine was introduced at a rapid rateand, when the solution turned yellow, a sunlamp was lit. The flow ofchlorine and the intensity of the light were adjusted so that thesolution remained yellow and the temperature did not exceed 80° C.during the first few hours of chlorination. Later, the temperature couldbe increased to 100°-120° C.

Periodically, a sample of the reaction mixture was analyzed by gaschromatography. The chlorination was continued until gas chromatographyshowed that incompletely chlorinated intermediates were absent in theproduct. The product was distilled at a reduced pressure on a wateraspirator. After the removal of chlorine and hydrogen chloride, thedistillation could be continued using a high vacuum pump.

Tetrachloroethylene carbonate boils at 46° C. at about 666 Pa. The pureproduct was recovered in yields as high as 94%.

(b) 4,4,5,5-Tetrachloro-2,2-difluoro-1,3-dioxolane (4)

A 360 mL "Hastelloy" C. shaker tube was charged with 113 g (0.5 mole) oftetrachloroethylene carbonate, sealed under nitrogen, cooled in a dryice acetone mixture, evacuated, flushed with nitrogen, reevacuated andcharged with 18 g (0.9 mole) of hydrogen fluoride and 194 g (1.8 mole)of sulfur tetrafluoride. The tube was agitated for 10 hours at 200° C.The tube was next chilled in an ice-water bath and then slowly vented toremove the excess SF₄ and HF. The product was dumped from the tube intowet ice and allowed to stand a day. The organic phase was separated fromthe aqueous phase in a polyethylene separatory funnel, then stirred witha 30% aqueous solution of potassium carbonate to neutralize free acid.The product was dried over potassium carbonate and distilled at areduced pressure. It boils at 126° C. at atmospheric pressure. The bestyield of 4,4,5,5-tetrachloro-2,2,-difluoro-1,3-dioxolane was 73%.Infrared and nuclear magnetic resonance (NMR) spectra support thechemical structure (4) of this dioxolane.

(c) 4,5-Dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (5)

A 500 mL, 3-neck, borosilicate, round bottom flask equipped with amechanical stirrer, water condenser topped by a small dry ice trap, anitrogen bubbler, and a thermometer was charged with 193 g (1.08 moles)of SbF₃, 124 g (0.415 mole) of SbCl₅, and 99 g (0.4 mole) of4,4,5,5-tetrachloro-2,2-difluoro-1,3-dioxolane. The stirred reactantswere heated to reflux with vigorous agitation for 7 hours.

The flask contents were distilled directly from the residual solidantimony salts at reduced pressures down to about 130 Pa with slightheating of the flask at the end of the distillation. The distillate wasthen extracted with two 10 mL portions of 21% aqueous hydrochloric acidafter which it was distilled from solid K₂ CO₃ or molecular sieves.

The best yield was over 90%, but yields were erratic. The pure productboils at 49° C. at atmospheric pressure. Infrared and NMR analysessupport the chemical structure of this dioxolane.

(d) Perfluorodioxole (PD) (1)

A 300 mL distilling flask with two side arms, equipped with a magneticstirrer, a thermometer, a syringe needle entrance, and a distillingcolumn topped by a water condenser and a dry ice condenser arrangementleading to a stainless steel cylinder collector in series with anitrogen bubbler, was charged with 7.3 g (0.3 mole) of magnesiumturnings, 0.2 g (0.00074 mole) of mercuric chloride, 0.2 g (0.00079mole) of iodine, and 80 mL (1 mole) of tetrahydrofuran.

The mixture was heated to about 60°-65° C., and the color of the mixturechanged from red to gray. 4,5-Dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane(21.5 g, 0.1 mole) was pumped into the flask through a syringe needle atthe rate of 0.24 mL/min. After the introduction of about 4 mL, themixture turned dark, and the reaction heat was sufficient to causevigorous refluxing in the dry ice condenser. The product,perfluorodioxole, was distilled from the mixture at about -5° to +5° C.(head temperature) and collected in the stainless steel cylinder.

Crude PD can be purified by slowly passing it through a cold 2% aqueoussolution of potassium carbonate and through cold water to removetetrahydrofuran and other water-soluble impurities, then collecting thepurified PD in a glass container maintained at a dry ice temperature. PDis best dissolved in 1,1,2-trichloro-1,2,2-trifluoroethane and kept insolution at a low temperature until needed. The solutions can be used inpolymerization reactions.

Alternative synthesis of perfluorodioxole (a) Hexachloro-1,3-dioxolane(7)

A 300 mL creased, 3-neck borosilicate flask equipped with a thermometer,a gas inlet tube, and a water condenser topped by a dry ice condenserleading to a drying tower and and then to a water scrubber was chargedwith 37 g (0.5 mole) of 1,3-dioxolane and 200 g (1.07 mole) of1,1,2-trichloro-1,2,2-trifluoroethane. After purging the system withnitrogen, chlorine gas was introduced into the flask at 19° C. Thesolution was then irradiated with a mercury vapor ultraviolet lamp. Therate of chlorine flow was such that the solution was yellow at all timesand the illuminaton intensity was regulated so that the temperature didnot rise above 35° C. during the first few hours of chlorination. Thechlorination was continued for 21 hours while the maximum temperaturewas maintained between 44° and 50° C. The1,1,2-trichloro-1,2,2-trifluoroethane and small amounts of chlorine andhydrogen chloride were distilled off at the pressure of a wateraspirator. The crude product was extracted with distilled watercontaining a small amount of tetrahydrofuran, then again with water,finally stirred with solid potassium carbonate. The product was thendistilled at a pressure of about 133 Pa and a temperature of 29° C. toyield 52.8 g of (7); the infrared absorbance spectrum was consistentwith the chemical structure of this dioxolane.

(b) 4,5-Dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (5) First Alternative

A 250 mL, 3 neck, round bottom flask equipped with a mechanical stirrer,thermometer and a reflux condenser leading to a dry ice trap under 0.1MPa of nitrogen was charged with 107.3 g (0.6 mole) of antimonytrifluoride and 69.4 g (0.232 mole) of antimony pentachloride. Themixture was stirred and hexachloro-1,3-dioxolane, 28 g (0.1 mole), wasintroduced into the flask by syringe; the flask was heated to 55° C.,but the temperature gradually dropped to 49° C. Heating was continuedfor 7 hours. The product was distilled through a short Vigreux column atroom temperature and pressures gradually decreasing to about 260 Pa andwas collected in a receiver cooled with dry ice. The distillate wasextracted twice with 5 mL portions of 21% aqueous hydrochloric acid andredistilled at a reduced pressure from solid potassium carbonate to give6.9 g of a clear, colorless, liquid product. Its infrared and NMRspectra were consistent with the chemical structure of (5).

Second Alternative

A 330 mL "Hastelloy" C shaker tube was charged under anhydrousconditions with 81.3 g (0.33 mole) of4,4,5,5-tetrachloro-2,2-difluoro-1,3-dioxolane, 9.0 g (0.03 mole) ofSbCl₅, and 20 g (1 mole) of hydrogen fluoride. The tube was heated to70° C. and mechanically shaken for 7 hours. After cooling to roomtemperature the product was washed with distilled water, then with anaqueous 10% solution of sodium carbonate, and finally distilled to yield19.5 g of a clear, colorless liquid product. Gas chromatography showedthat 67% of this product was the desired4,5-dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane (5), while about 25% was4,4,5-trichloro-2,2,5-trifluoro-1,3-dioxolane, and about 8% of othermaterials, most of them higher boiling. The dioxolane (5), which boilsat 46° C. at atmospheric pressure, can be separated by fractionaldistillation from the trichlorotrifluorodioxolane (b.p. 83°-84° C.) andthe other contaminants, which also include some unchanged startingdioxolane (4).

(c) Perfluoro-1,3-dioxole (1)

The same method of dechlorination is used as described above under"Synthesis of PD", step (d).

Amorphous Copolymers of PD with TFE

A 110 mL stainless steel shaker tube was charged with 120 g (0.64 mole)of 1,1,2-trichloro-1,2,2-trifluoroethane, 7.0 g (0.049 mole) of PD,0.015 g (0.000046 mole) of perfluoropropionyl peroxide, 0.08 mL ofcyclohexane, and 3 g (0.03 mole) of TFE. The tube was agitated one hourat 50° C. and one hour at 55° C. After cooling and discharging thecontents, the unchanged monomers and the1,1,2-trichloro-1,2,2-trifluoroethane were distilled off, and thepolymer remaining in the tube was dried in a vacuum oven at 110° C. Theyield was 4.7 g of colorless material (a 47% conversion), which wasfound by NMR spectroscopy to be a copolymer of 81.7 mole % of PD and18.3 mole % of TFE. It had a Tg of 135° C.; its 230° C. melt viscositywas 1.42×10³ Pa.s.

Additional amorphous copolymers of PD with TFE were obtained by the sametechnique from different proportions of the starting monomers and atdifferent conversions. The following table summarizes those runs:

                  TABLE 1                                                         ______________________________________                                                     Polymer                                                          Monomer                        Melt                                           PD    TFE    Conver-   PD    TFE         Viscosity                            Mole  Mole   sion      Mole  Mole Tg °C.                                                                        (Pa · s at                  %     %      %         %     %    %      230° C.)                      ______________________________________                                        100   0      82        100   0    173,212                                                                              --                                   61.8  38.2   47        81.7  18.3 135    1.42 × 10.sup.3                55.0  45.0   56        75    25   124    5.8 × 10.sup.3                 62.7  37.3   60        76.1  23.9 125    2.68 × 10.sup.4                64.4  35.6   65        --    --   131    3.0 × 10.sup.4                 59.0  41.0   46        --    --   130    1.4 × 10.sup.3                 ______________________________________                                    

The following physical properties were determined at 23° C./50% relativehumidity for the 76.1/23.9 PD/TFE copolymer of Table 1:

                  TABLE 2                                                         ______________________________________                                        Modulus (MPa)       1703                                                      From stress/strain plot                                                       Stress (MPa) ASTM D1708                                                       Yield               43.4                                                      Maximum             43.4                                                      Break               43.4                                                      Strain (%) ASTM D1708                                                         Yield               5.9                                                       Break               19.9                                                      ______________________________________                                    

The modulus and stress values for these amorphous perfluorodioxolecopolymers are higher than reported in the literature for any otherperfluorocarbon resin. In addition, these copolymers have an outstandingcut through resistance and low creep characteristics for perfluorocarbonresins, which makes them useful in electrical insulation and in variousmechanical parts.

Crystalline Copolymers of PD with TFE

A 110 mL stainless steel shaker tube was charged with 110 g (0.59 mole)of 1,1,2-trichloro-1,2,2-trifluoroethane, 1.5 g (0.01 mole) of PD, 0.03g (0.000075 mole) of bis(4-t-butylcyclohexyl) peroxydicarbonate, and 10g (0.1 mole) of TFE. The tube was agitated for 3 hours at 55°-65° C. Theunpolymerized monomers were vented, and the polymer suspension wastransferred to a 355 mL stainless steel shaker tube, which was chargedwith 0.2 g of water and pressurized to 1.1 MPa with a mixture of 25 vol.% of fluorine and 75 vol. % of nitrogen. The tube was agitated 8 hoursat 200° C. The clear solvent was decanted after cooling. The residualpolymer was dried. It weighed 6.2 g. The above fluorination step wasnecessary to break up the difficultly filterable suspension of thepolymer in the solvent. The polymer had a melting point of 309° C., asdetermined by differential thermal analysis, and a melt viscosity of6.8×10³ Pa.s at 380° C.

Other crystalline copolymers of PD with TFE were prepared by thistechnique. Their melting points were in the range of 306°-326° C. In allcases the amount of PD incorporated into the copolymer was less thanabout 12 mole %. When the amount of PD was increased beyond this value,the copolymers were either substantially or completely amorphous.

The copolymer melting at 309° C. was pressed at 380° C. into a thinfilm. The tensile properties of this film were compared with those of afilm made from a commercial resin, "Teflon" PFA 350, which is afluorocarbon copolymer having perfluoroalkoxy side chains. The resultsare shown in the following table:

                  TABLE 3                                                         ______________________________________                                                     Polymer of                                                                    TFE/PD "Teflon" PFA 350                                          ______________________________________                                        Melting point (°C.)                                                                   309      306                                                   Stress (MPa)                                                                  Yield          15.2     15.2                                                  Maximum        23.4     23.4                                                  Break          23.4     23.4                                                  Strain (%)                                                                    Yield          4.9      20.7                                                  Break          210.4    326.3                                                 ______________________________________                                    

As can be seen, the TFE/PD copolymer of this invention has the sametensile strength as the commercial resin but lower elongation.

An Elastomeric Terpolymer of PD, Vinylidene fluoride and TFE

A 110 mL stainless steel shaker tube is charged with 100 g of1,1,2-trichlorotrifluoroethane, 2.0 g of PD, 0.02 g ofbis(4-t-butylcyclohexyl) peroxydicarbonate, 6.0 g of vinylidene fluorideand 5.0 g of TFE. The polymerization is carried out under autogeneouspressure for 3 hours at 55°-65° C. After cooling, the tube contents aretransferred to a still; after distilling off the unchanged monomers andtrichlorotrifluoroethane a white, solid polymer, 5.1 g, is obtained. Aportion of the polymer is compression formed at 230° C. to give a thin,tough, elastomeric, clear, self supporting film.

A Crystalline Terpolymer of PD, Ethylene and TFE

A 110 mL stainless steel shaker tube is charged with 100 g of1,1,2-trichlorotrifluoroethane, 1.0 g of PD, 0.03 g ofbis(4-t-butylcyclohexyl) peroxydicarbonate, 1.0 g of ethylene and 12 gof TFE. The agitated tube is heated at 55°-65° C. for three hours underautogenous pressure. Following the polymerization thetrichlorotrifluoroethane and unchanged monomers are distilled offleaving 9.8 g of a white crystalline solid. This polymer is compressionformed at 350° C. into thin, tough, plastic films.

An amorphous terpolymer of PD,2-[1-[difluoro[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoroethanesulfonylfluoride, and TFE

A 110 mL stainless steel shaker tube is charged with 100 g of1,1,2-trichlorotrifluoroethane, 0.03 g ofbis(4-t-butylcyclohexyl)peroxydicarbonate, 4 g of PD, 10 g of TFE, and 1g of2-[1[difluoro[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2-tetrafluoroethanesulfonylfluoride. The tube is agitated and the polymerization is carried out at55°-65° C. under autogenous pressure for three hours. After distillingoff the unchanged monomers and trichlorotrifluoroethane, there isobtained 10.2 g of a white, granular, solid polymer. This polymer iscompression formed at 230° C. into a thin, tough, transparent film. Thepolymer has no crystalline melting point and thus is amorphous.

Homopolymer of PD

(a) A 110 mL stainless steel shaker tube was charged with 120 g of1,1,2-trichloro-1,2,2-trifluoroethane, 0.02 g of perfluoropropionylperoxide, and 6.2 g of PD (purified by water scrubbing) and heated for 3hours with agitation at 50°-55° C. After cooling to room temperature,the tube was discharged; the solvent was distilled off, and the solidwas dried at 110° C. in a vacuum oven to give 5.1 g of a homopolymerwhich exhibited Tg's at 173° C. and 212° C. The absence of a crystallinemelting point and X-ray analysis demonstrated that the polymer wasamorphous. The PD homopolymer was compression formed at 340° C. into afilm which had the following tensile characteristics, determined at 23°C./50% relative humidity:

                  TABLE 4                                                         ______________________________________                                        Modulus (MPa)       1373                                                      From stress/strain plot                                                       Stress (MPa) ASTM D1708                                                       Yield               49                                                        Maximum             49                                                        Break               49                                                        Strain (%)          4.9                                                       Break                                                                         ______________________________________                                    

(b) In the homopolymerizaton of PD which was distilled but notwater-scrubbed (and thus contained a minor amount of tetrahydrofuran),the solid polymer formed under similar conditions had low Tg's, withinthe range of 84°-92° C. It was determined by infrared analysis that asmall amount of THF was incorporated in the polymer chain.

(c) Small amounts of tetrahydrofuran (say, 10 to 100 vol. % of PD)inhibit homopolymerization of PD to solid homopolymer during storage.However, low molecular weight polymers or oligomers of PD formedspontaneously on standing at room temperature. These were liquids fromwhich unpolymerized PD could be readily separated by distillation. Theselow molecular weight polymers were readily identifiable by theircharacteristic infrared spectra, which were consistent with a chemicalstructure containing perfluorodioxole units as well as tetrahydrofuranunits.

Utility of PD/TFE Copolymer as a Coating

A mild steel wire was immersed in concentrated hydrochloric acid;chemical attack on the wire was evident in less than 10 seconds by theformation of bubbles on the wire. The wire was removed from the acid,washed with water and dried. A solution of 1 g of a 125° C. Tg TFE/PDcopolymer in 20 mL "Fluorinert Electronic Liquid" FC75 (a 3M product)was made by shaking the polymer in the liquid. The wire was thendip-coated with this solution and dried at 90° C. in a vacuum oven. Thecoated wire when immersed in concentrated hydrochloric acid for severalminutes was not attacked.

A section of soft wood was similarly coated and dried. Immersion of thisin water for several minutes failed to show any water absorbance.However, uncoated wood absorbed water in less than 10 seconds.

I claim:
 1. 4,5-Dichloro-2,2,4,5-tetrafluoro-1,3-dioxolane.